The present invention relates to a roller, particularly a hot roller, which is reinforced with a working jacket of a hard metal or the like, and particularly a roller in which the working jacket is prestressed by a compression pressure applied in the direction of the longitudinal axis of the roller via clamping rings which have clamping surfaces that are arranged at an angle with respect to the roller body, and the working jacket and roller body being separated by an annular gap of sufficient height to prevent the facing peripheral surfaces of the jacket and the roller body from coming into contact with one another during operation of the roller.
German Patent Application No. P 2,618,884.1 filed on Apr. 29, 1976, and a corresponding U.S. application, Ser. No. 791,299, filed by Heinz Zimmermann and Wolfgang Martens on Apr. 27, 1977, entitled PROCESSING ROLLER HAVING REINFORCING JACKET OF HARD METAL, and claiming the priority of the above-mentioned German application, discloses a roller, particularly a hot roller, which is reinforced with a working jacket of hard metal or the like which is compressively prestressed by pressure in the direction of the longitudinal axis of the roller via clamping rings which have clamping surfaces that are inclined with respect to the roller axis. That roller is characterized in that a continuous annular gap is disposed between the working jacket and the roller body and has a radial dimension such that during operation of the roller within its design operating temperature range the outer peripheral surface of the roller body and the inner peripheral surface of the working jacket do not contact one another.
The purpose of this arrangement is to isolate the working jacket from the mechanical stresses which are produced during operation of the roller as a result of the roller body being heated and to prevent the working jacket from being torn apart by such stresses. Such an arrangement is advisable, particularly for hot rollers which are heated to higher operating temperatures, since the coefficient of thermal expansion of steel, the material of the roller body, is about 13-18 .multidot. 10.sup.-6 .multidot. degree.sup.-1 and that of hard metal is about 5-7.5 .multidot. 10.sup.-6 .multidot. degree.sup.-1.
If, during operation of the roller, the working jacket expands in a radial direction, the clamping bodies which position the working jacket naturally follow this expansion. In order to prevent the working jacket from coming loose, since it does not sit directly on the roller body due to the above-mentioned annular gap, at least one resiliently deformable member is provided in a known manner between the working jacket and an abutment so as to shift the clamping rings in the direction of the longitudinal axis of the roller in correspondence with the expansion of the working jacket.
The structure disclosed in the above-cited applications is based on the assumption that the angle formed between those surfaces of a clamping ring which bear, respectively, against the working jacket and the outer periphery of the roller body, or formed between a surface of the working jacket which bears against a clamping ring and the outer peripheral surface of the working jacket, should invariably be an obtuse angle so that when the roller body expands no additional radially outwardly acting forces are transferred to the working jacket. The reason for this was stated in the above-cited applications to be that hard metal is able to absorb extraordinarily high friction and pressure stresses but, due to its relatively soft cobalt matrix, is less able to support tensile stresses.
The arrangement disclosed in the above-cited applications operates perfectly as long as it is assured that even with the slightest change in the operating temperature the clamping rings are instantaneously adjusted and as long as the force P imposed on the working jacket by the workpiece is not too high. If these conditions are not met, there exists the danger, for example, that, when the temperature of the roller body increases, which is unavoidable during long periods of operation, the clamping effect will lessen and the working jacket will become loose and begin to knock. The result is that the workpieces are rolled to dimensions which are outside the preset tolerance limits and there exists the additional danger that the working jacket might be damaged.
The limits for the roller pressures are determined by the bending elasticity of the working jacket and of the clamping rings. The structure disclosed in the above-cited applications thus makes it necessary that the roller pressures P be transferred around the roller body so that they can be absorbed by the clamping rings only on the side of the roller diametrically opposite the working side. Thus the working jacket is continuously subjected to a milling pressure which, although slight, is tolerable only up to a given maximum roller force P.